Temporal variation in leachate composition of a newly constructed landfill site in Lahore in context to environmental pollution and risks

Abstract

This study investigated the seasonal and temporal variations in the extent and source of physiochemical and toxic trace elements in the Lakhodair landfill site of Lahore, Pakistan. For this purpose, systematic composite samples were collected every month, consecutively for 1 year, and analyzed for different physiochemical parameters and trace elements. The results of TDS, TSS, COD, NH₃-N, BOD₅, sulfate, sulfides, phenolic compounds, and oil and grease were higher than the national environmental quality standard (NEQs). The concentrations of trace elements, especially Mn (1.7 mg/L) and Cd (0.05 mg/L), were above the MPL, while Fe (14 mg/L), Ni (1.6 mg/L), and Zn (6.7 mg/L) were also found higher than the NEQs in some samples. In Lakhodair leachates, the TDS, COD, NH₃-N, BOD₅, sulfides, and Cl^- have high concentration coefficient (i.e., CC 3 to > 6), which falls in the category of considerable to high contamination and risk level, while the remaining parameters were in the category of low to moderate contamination (CC 1 to ≤ 3) and moderate risk. The lower BOD₅/COD ratio (< 0.1) in spring and autumn seasons represents the active methanogenesis and anaerobic activities in the Lakhodair landfill site. The anaerobic and methanogenesis activities enhance the redox reaction as a result of CO₂ emission, which increases the pH, TDS, COD, Cl^-, BOD₅, NH₃-N, sulfides, and phenolic compounds in the leachate site. However, the lower concentrations of some trace elements in leachate may be because of an anaerobic process that may immobilize the trace elements. It is presumed that the trace elements in the Lakhodair landfill may be in a metastable state, which is difficult to leach out. It is hereby recommended that leachate produced in the Lakhodair landfill site should be handled carefully to limit the environmental and health implications.

Keywords: Lakhodair; Landfill site; Methanogenesis; Phenolic compounds; Seasonal and temporal variation; Solid wastes; Trace elements.